1. Field of the Invention
The present invention is directed to a fiber optic vibration sensor and, more particularly, to a sensor which phase modulates a light beam responsive to the vibration of a load mass.
2. Description of the Related Art
Prior art fiber optic vibration sensors which are available from Westinghouse Electric Corporation and ASEA provide a relatively narrow bandwidth. The Westinghouse vibration sensor interrupts the light beam from a optical fiber using a vibrating screen carried by a resonantly tuned reed. The ASEA sensor specularly reflects a light beam off of a cantilevered beam which also has a resonant operating point. Amplitude modulation of the light beam occurs in the ASEA sensor because the bending cantilevered beam allows a portion of the light to escape that is, not be reflected back down the fiber). Within their narrow bandwidth the sensors can be dramatically non-linear because of the resonant tuning, thereby requiring the application of non-linear amplifiers and filters to the acceleration signal produced by the accelerometer, if the monitor which senses the light beam is not properly calibrated. These prior art sensors also have a temperature drift coefficient of from 12-36% making the sensors impractical for environments where the temperature changes.